In the early 1900s, many kids in coal mines.

When America entered the 1900s, coal was the energy mainstay for the nation's businesses and industries. Coal stayed America's number one energy source until the demand for petroleum products pushed petroleum to the front. Automobiles needed gasoline. Trains switched from coal power to diesel fuel. Although breaker boys were primarily children, elderly coal miners who could no longer work in the mines because of age, disease, or accident were also sometimes employed as breaker boys. The use of breaker boys began in the mid-1860s.

The common sense pamphlet i think